1. Field of the Invention
The present invention pertains to telecommunications, and particularly to the relocation of a Serving Radio Network Controller in a Radio Access Network.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks)
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC (see, in this regard, U.S. patent application Ser. No. 09/035,821 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Measurement Transfer”; and U.S. patent application Ser. No. 09/035,788 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Congestion Control”, both of which are incorporated herein by reference). The interface between a SRNC and a DRNC is termed the “Iur” interface.
In the Universal Mobile Telecommunications (UMTS), a service is identified on a non-access stratum level of the UMTS architecture by a Non-Assess Stratum (NAS) Service Identifier (NAS Service ID). On the access stratum level of the UMTS architecture, each service is identified by a radio access bearer (RAB) identifier (RAB ID) on the Iu interface and by one or more radio bearer (RB) identifiers (RB IDs) on the radio interface (e.g,. the air interface). Each NAS Service is thus linked to one radio access bearer (RAB), and each radio access bearer (RAB) is linked to one or more radio bearers (RBs). One or more radio bearers (RBs) are linked to one transport channel, e.g., to one Dedicated Transport Channel (DCH) on the Iur, Iub, and radio interfaces. Each DCH is thus linked to one or more radio bearers (RBs). Consequentially, each radio access bearer (RAB) is linked to one or more DCHs.
A Dedicated Transport Channel (DCH) is identified by a DCH ID on the Iur and Iub interfaces. The DCH ID used on the Iur and Iub interfaces is not used on the radio interface. Instead, a Transport Channel (TrCH) identifier is used over the radio interface to identify the transport channel on the radio interface. The serving RNC (SRNC) and the UE know this Transport Channel (TrCH) identifier (in the same way as they know the RB ID), but the Transport Channel (TrCH) identifier is not known to the DRNC or to the Base Station.
A project known as the Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies. The 3GPP anticipates a situation in which the role of a Serving RNC (SRNC) will be relocated from a first RNC to another RNC, such as an RNC which previously served as a Drift RNC (DRNC). In connection with such relocation, the 3GPP proposes to signal from the first RNC (e.g., the old SRNC) to the second RNC (e.g., new SRNC) certain linking information, and specifically to signal information which links the radio access bearer (RAB) IDs and their radio bearer (RB) IDs. However, in accordance with this 3GPP proposal, the new SRNC must still guess which transport channels would correspond to the radio bearers utilized.
What is needed, therefore, and an object of the present invention, is a technique for enabling the new SRNC to link transport channels with radio bearers.